The present invention relates to a system for controlling air-fuel ratio of mixture for an automotive engine, and more particularly to a learning control system for updating data stored in a table for the learning control.
In the learning control system, the updating of data is performed with new data obtained during the steady state of engine operation. Accordingly, means for determining whether the engine operation is in steady state is necessary. A conventional learning control system (for example U.S. Pat. No. 4,309,971) has a matrix (two-dimensional lattice) comprising a plurality of the divisions, each representing engine operating variables such as engine speed and engine load. When the variables continue for a predetermined period of time in one of divisions, it is determined that the engine is in steady state. On the other hand, a three-dimensional look-up table is provided, in which a matrix coincides with the matrix for determining the steady state. Data in the look-up table is updated with new data obtained during steady states.
In such a system if a sensor for obtaining information for updating data deteriorates and fails to produce a proper output signal, old data are rewritten by improper data. In case of a learning control system for controlling the air-fuel ratio of air-fuel mixture for a motor vehicle, an O.sub.2 -sensor is employed for obtaining information of the air-fuel ratio. If the O.sub.2 -sensor does not produce a proper output signal, the driveability of the vehicle decreases and fuel consumption increases.